The invention relates to catalyst systems useful in hydrocarbon upgrading processes and to methods for their production and use. In another aspect, this invention relates to processes for converting oxygenated hydrocarbons to C.sub.2 -C.sub.4 olefins with an increase in olefin selectivity and a reduction in coke formation resulting from the conversion of such oxygenated hydrocarbons in the presence of such catalyst systems. The term "oxygenated hydrocarbons" as employed herein comprises hydrocarbons containing aliphatic moieties such as, but not limited to, alcohols, halides, mercaptans, sulfides, amines, ethers, and carbonyl compounds (aldehydes, ketones, carboxylic acids and the like) or mixtures thereof.
It is known to convert oxygenated hydrocarbons to olefins in the presence of catalysts which contain a silicoaluminophosphate (SAPO), as is described in U.S. Pat. Nos. 4,861,938, 5,475,182, 5,248,647 and 5,663,471, each incorporated herein by reference.
One concern with the use of SAPO catalysts in the conversion of oxygenated hydrocarbons to olefins is the excessive production of coke during the conversion reaction. Coke formed during the SAPO catalyzed conversion of oxygenated hydrocarbons tends to cause catalyst deactivation. It is desirable to improve processes for the conversion of oxygenated hydrocarbons to olefins by minimizing the amount of coke formed during such processes. It is also desirable to have a SAPO catalyst that is useful in producing significant quantities of olefin conversion products.